[udpclient] doesn't output connection information nor received data when using broadcast address

[avilleret]

When I'm connecting to an UDP server with it's IP address, it answer with "acknowledge"
when I'm connection with a broadcast IP (i.e. 192.168.0.255) I didn't not receive the answer, but a python script does.

My UDP server run on a Atmega 328P with an Ethernet shield, here the code :

/*
 UDPSendReceiveString:
 This sketch receives UDP message strings, prints them to the serial port
 and sends an "acknowledge" string back to the sender

 A Processing sketch is included at the end of file that can be used to send
 and received messages for testing with a computer.

 created 21 Aug 2010
 by Michael Margolis

 This code is in the public domain.
 */


#include <EthernetUdp.h>

// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = {
  0x98, 0x76, 0xB6, 0x11, 0x18, 0x30
};

unsigned int localPort = 8888;      // local port to listen on

// buffers for receiving and sending data
char packetBuffer[UDP_TX_PACKET_MAX_SIZE];  // buffer to hold incoming packet,
char ReplyBuffer[] = "acknowledged";        // a string to send back

// An EthernetUDP instance to let us send and receive packets over UDP
EthernetUDP Udp;

void setup() {
  
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  // start the Ethernet connection:
  Serial.println("Initialize Ethernet with DHCP:");
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
    if (Ethernet.hardwareStatus() == EthernetNoHardware) {
      Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
    } else if (Ethernet.linkStatus() == LinkOFF) {
      Serial.println("Ethernet cable is not connected.");
    }
    // no point in carrying on, so do nothing forevermore:
    while (true) {
      delay(1);
    }
  }
  // print your local IP address:
  Serial.print("My IP address: ");
  Serial.println(Ethernet.localIP());
  
  // start UDP
  Udp.begin(localPort);
}

unsigned long count = 0;

void loop() {
  // if there's data available, read a packet
  int packetSize = Udp.parsePacket();
  if (packetSize) {
    Serial.print("Received packet of size ");
    Serial.println(packetSize);
    Serial.print("From ");
    IPAddress remote = Udp.remoteIP();
    for (int i=0; i < 4; i++) {
      Serial.print(remote[i], DEC);
      if (i < 3) {
        Serial.print(".");
      }
    }
    Serial.print(", port ");
    Serial.println(Udp.remotePort());

    // read the packet into packetBufffer
    Udp.read(packetBuffer, UDP_TX_PACKET_MAX_SIZE);
    Serial.println("Contents:");
    Serial.println(packetBuffer);

    // send a reply to the IP address and port that sent us the packet we received
    Udp.beginPacket(Udp.remoteIP(), Udp.remotePort());
    Udp.write(ReplyBuffer);
    Udp.endPacket();
  }
  delay(10);
}

.
You will find the client.py and client.pd script that demonstrate the issue.
But you'll need an arduino and an ethernet shield to reproduce it.
client-issue.tar.gz
Unfortunately I could not reproduce exactly the same behavior with a Python script as UDP server

[avilleret]

wireshark shows that the server is replying well with the same message as if broadcast is disabled
but client says that Destination unreachable (Port unreachable)

so I tried to add an UDP receive on that port, but Pd says that the port is already in use.

[avilleret]

finally I got a very simple but working udpclient / udpserver pair in plain C that demonstrate the issue.

I found the code here : http://www.cs.ubbcluj.ro/~dadi/compnet/labs/lab3/udp-example1-c.html
I tuned it to work with broadcast.
iemnet-issue9.tar.gz

You'll find the modified udpclient.c and udpserver.c as well as a client.pd patcher.
I ran the server with ./udpserver 8888
When running udpclient with ./udpclient 192.168.0.5 8888 I got an acknowledgement after sending some string.
I got the same acknowledgement when starting with 192.168.0.255 broadcast IP.

But with client.pd, I got the acknowledgement only when I connect with unicast IP but not with broadcast.

[avilleret]

hum... injecting the following code before the connect call works, but not after

  post("snd some data...");
  char buffer[256];
  sprintf(buffer, "c'est la fête!\n");

  int length=sizeof(struct sockaddr_in);

  int n=sendto(sockfd,buffer,strlen(buffer),0,&server,length);

  if (n < 0) error("Sendto");

  struct sockaddr_in from;

  n = recvfrom(sockfd,buffer,256,0,&from, &length);

  if (n < 0) error("recvfrom");

  post("Got an ack: %s",buffer);
  post("done");

commenting the connect() block make it work again but in that case, the answer is never fired in the left outlet.

[umlaeute]

confirmed.